1. Field of the Invention
The present invention relates to a read/write technology of compact disks, and more particularly to a method of correcting a clock of a compact disk and a circuit thereof.
2. Description of the Related Art
As to various storage mediums for computers, compact disk (CD) has the advantages of high storage capacity, low cost and high portability, and has been widely used in the field. When data are stored in a CD, eight-to-fourteen modulation (EFM), reed-soloman modulation and interleave method is applied to process the data. The EFM means that 8-bit data are transformed into 14-bit data on a CD. 8-bit data are transformed into 16-bit data on a digital versatile disc (DVD) and stored therein.
When the data are read, radio frequency data (RF DATA) are generated from sensing the reflective laser from the CD. According to the RF DATA, the data signal DSEFM and the clock signal EFMCLK are generated. Then, a decoding of the two signals process is performed for the subsequent signal decoding process.
Because of the high-capacity, high read/write and high precision requirement for the CD, technologies, such as EFM, for improving the read/write reliability have been widely used. In order to read the data correctly, a sync pattern is put between the data. Because the data read out are a series of signals, the signals should be precisely read according to the clock signal. If the clock signal is not correct, the data signal DSEFM will be falsely decoded. Therefore, the clock signal EFMCLK should be kept in correct frequency. Prior art technologies use self frequency-lock to decode the data. CD is made from plastic and is vulnerable to scratches. If the scratch causes a defective region on CD, the prior technology does not perform self frequency-lock function. When the data in the defective region are read, the clock signal EFMCLK holds on to the last frequency of the non-defective region. Because of the failure of the self frequency-lock, the frequency of the clock signal EFMCLK shifts. After leaving the defective region, the read of the DSEFM is according to the false clock signal EFMCLK. Therefore, the data read is, of course, are not correct.